UML 2.0 in a Nutshell

Messages

The focus of interaction diagrams is on the communication between lifelines. This communication can take many different forms: method calls, sending a signal, creating an instance, destroying an object, etc., all of which are collectively called messages . A message specifies the kind of communication, its sender, and its receiver. For example, a PoliceOfficer class instantiating a SpeedingTicket class is represented as a message from an instance of PoliceOfficer to the newly created instance of SpeedingTicket.

The most common use of messages is to represent method calls between two objects. When messages are used to indicate a method call, you can show the parameters passed to the method in the message syntax. The parameters should be one of the following:

• Attributes of the sending object

• Constants

• Symbolic values (expressions showing what the legal values can be)

• Explicit parameters of the enclosing interaction

• Attributes of the class owning the enclosing interaction

The syntax for a message is:

            
    attribute = signal_or_operation_name (arguments) : return_value

where:

attribute

Is an optional part of the syntax that provides a shorthand way of showing that the return value from this message is stored in the specified attribute. The attribute must be an attribute of the lifeline sending the message, a global attribute of the interaction, or an attribute of the class owning the interaction.

signal_or_operation_name

Specifies the name of the operation to ...